lib/rtc-lib.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * rtc and date/time utility functions
   4  *
   5  * Copyright (C) 2005-06 Tower Technologies
   6  * Author: Alessandro Zummo <a.zummo@towertech.it>
   7  *
   8  * U-Boot rtc_time differs from Linux rtc_time:
   9  * - The year field takes the actual value, not year - 1900.
  10  * - January is month 1.
  11  */
  12
  13 #include <rtc.h>
  14 #include <linux/math64.h>
  15
  16 static const unsigned char rtc_days_in_month[] = {
  17         31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
  18 };
  19
  20 #define LEAPS_THRU_END_OF(y) ((y) / 4 - (y) / 100 + (y) / 400)
  21
  22 /*
  23  * The number of days in the month.
  24  */
  25 int rtc_month_days(unsigned int month, unsigned int year)
  26 {
  27         return rtc_days_in_month[month] + (is_leap_year(year) && month == 1);
  28 }
  29
  30 /*
  31  * rtc_to_tm - Converts u64 to rtc_time.
  32  * Convert seconds since 01-01-1970 00:00:00 to Gregorian date.
  33  *
  34  * This function is copied from rtc_time64_to_tm() in the Linux kernel.
  35  * But in U-Boot January is month 1 and we do not subtract 1900 from the year.
  36  */
  37 void rtc_to_tm(u64 time, struct rtc_time *tm)
  38 {
  39         unsigned int month, year, secs;
  40         int days;
  41
  42         days = div_u64_rem(time, 86400, &secs);
  43
  44         /* day of the week, 1970-01-01 was a Thursday */
  45         tm->tm_wday = (days + 4) % 7;
  46
  47         year = 1970 + days / 365;
  48         days -= (year - 1970) * 365
  49                 + LEAPS_THRU_END_OF(year - 1)
  50                 - LEAPS_THRU_END_OF(1970 - 1);
  51         while (days < 0) {
  52                 year -= 1;
  53                 days += 365 + is_leap_year(year);
  54         }
  55         tm->tm_year = year; /* Not year - 1900 */
  56         tm->tm_yday = days + 1;
  57
  58         for (month = 0; month < 11; month++) {
  59                 int newdays;
  60
  61                 newdays = days - rtc_month_days(month, year);
  62                 if (newdays < 0)
  63                         break;
  64                 days = newdays;
  65         }
  66         tm->tm_mon = month + 1; /* January = 1 */
  67         tm->tm_mday = days + 1;
  68
  69         tm->tm_hour = secs / 3600;
  70         secs -= tm->tm_hour * 3600;
  71         tm->tm_min = secs / 60;
  72         tm->tm_sec = secs - tm->tm_min * 60;
  73
  74         /* Zero unused fields */
  75         tm->tm_isdst = 0;
  76 }